Method of improving the bonding properties of steel surfaces



United States Patent METHOD OF IMPROVING THE BONDING PROPERTIES OF STEELSURFACES Paul H. Margulies, Buffalo, N.Y., assignor to Food Machineryand Chemical Corporation, San Jose,

No Drawing. Application April 13, 1956 Serial No. 577,936

4 Claims. (Cl. 41-42) This invention pertains to a method of improvingthe bonding properties of mild steel surfaces.

Usefulness, serviceability and attractiveness of steel surfaces,particularly those present in consumer goods, are almost invariablygreatly improved by application of a surface coating to these surfaces.In many cases such a surface coating is a necessary prerequisite,spelling the difference between a useful and a useless item.

The surfzce coatings considered here may be or anic coatin s, such aslacgu er, paint, retinous, rubber; and simt ar coatings, or they may beinorganic coatings, for examroplated metallic coatings or metalliccoatings applied by u n-electrolytic means. Not considered here and notwithin the scope of this invention are coatings applied at hightemperatures, such as hotdipped metallic coatings.

Any such coating is applied for the purpose of presenting to theenvironment, not a steel surface but the particular surfacecharacteristics of the coating. Therefore, such coatings shouldcompletely cover the underlying steel surface and do so reliably duringthe service life of the item. Of utmot importan"e in this ccnnection isthe ability of the coating to adhere firmly to the steel surface underservice condition. Ideally, the coating should be so firmly adherent,that a break, if it occurs at all, will be either in the steel or in thecoating, but not at the interface.

It has been recognized for a long time that the condition of the steelsurface, prior to the application of a coating, is of very greatimportance. Obviously, gross contamination of that surface bymanufacturing re'idues, such as oxide scale, rust, grease and the like,will interfere with proper coating adhesion. Therefore, surface cleaningby a variety of pro'cedures, to remove gross contamination, is standardpractice. In these procedures, solvents are employed for grease and oilremoval, acids, or alkalies for removal of other contaminants, and inmany cases multi-step treatments using various such cleaning agents areemployed. Generally, proper use of these and related procedures, so'memechanical in nature, will result in rather complete removal of gro"scontaminants and give a steel surface termed clean. Also, experience hasshown that coatings applied to such a clean steel surface will adherequite well to that surface. Therefore, industry quite generallyconcluded that cleaning procedures as illustrated above, if properlyused, will give a steel surface with the best bonding characteristicspractically obtainable.

More recent investigations, however, have shown that ideally cleansurfaces should have bonding characteristics vastly superior to thoseobtained with the usual, though carefully applied, cleaning methods.

It has now been found, in accordance with the present invention, that arelatively very simple treatment, applied to steel surfaces, after theusual grease and/or scale removal, will produce a surface with bondingcharacteristics vastly superior to those obtained by heretofore knowncleaning procedures and approaching the bonding characteristics ofideally clean surfaces.

The treatment of this invention employs a treating bath comprising anaqueous solution of acids and oxidizing agents. Based on the discoverythat in such systems, water must be regarded as an active reagent andnot simply as a diluent, the treating bath must contain water. acid oracids and the oxidizing agent in certain critical concentrations andratios to each other.

A typical bath, in accordance with my invention, might contain asessential ingredients, phosphoric acid, water and hydrogen peroxide.This bath will vastly improve bonding characteristics of mild steel bysimply contacting the steel with it at ambient temperature for from 20to 120 seconds, provided the bath constituents are present in certainconcentrations and ratios to each other.

An operable system of this type can be defined clearly by means of atriangular graph in which each apex of the triangle represents acomponent concentration of 100% and each side of the triangle acomponent concentration of zero percent.

In such a graph, suitable bath compositions will be found to be betweenapproximately 20 to weight percent of w ter, 5 to 30 weight percent of H0 and 25 to weight percent of mineral acid. The actual bath compositionis then defined by the further requirement that the sum of percentagesof water, H 0 and acid must equal 100%.

This relationship is therefore as follows:

Percent water+ percent H 0 +percent mineral acid=l00% (1) whereinPercent water is between 20% and 65% (2) Percent H 0 is between 5% and30% (3) Percent mineral acid is between 25% and 70% (4) Because resultsover the whole range are more or less the same, one will choose, forpractical reasons, systems re atively low in H 0 and/or mineral acid.For any system the proper percentage of water is then found fromEquation 1 by inserting the chosen percentage figures for the other twocomponents.

Out ide the specified range, results will become more and moreunsatisfactory, either in fact or in cost or both.

In making up the baths of this invention, one may employ a mineral acid.Practical considerations dictate the use of phosphoric acid or sulfuricacid, or a mixture thereof, as the acid component. However, sulfuricacid alone may be used, an example being a bath containing 40% water,42% H 50, and 18% H 0 Other mineral ac ds are less desirable because oftheir incompatibility with H 0 HC] for example reacting with liberatio'nof some chlorine. Mixtures of phosphoric acid and sulfuric acid are,however, advantageous and are preferred. In this case, bath compositionis calculated as explained above for phosphoric acid, but in actuallymaking up the bath, 5 to 20 percent of H PO as calculated, is replacedby H on a weight basis.

As oxidizing ingredient, it is preferred to use H 0 but compoundsliberating H 0 in contact with water in presence of acid may be used.

If desired, surface active agents may be added to the solution.

The steel to be treated must be free of grease and oil, and preferablyfree of mill scale. Particularly good results are obtained with coldrolled mild steel, but hot rolled steel will also respond to thetreatment after proper oxide scale remo'val.

After degreasing and, if needed, de-scaling, the steel. preferably aftera water rinse, is immersed in the treating bath at ambient temperature.Immersion time may range 3 from about to 30 seconds to as much as two orthree minutes and longer. Very good results can be obtained in about 30to 60 seconds and are not substantially improved with longer treatingtimes, which however may be more practical in certain cases.

Upon removal from the treating bath, the steel is rinsed promptly andthoroughly with cold water and dried. The improved brightened steelsurface obtained will not change its characteristics over prolongedperiods of time and may be coated immediately after drying, or days andweeks thereafter, without change in bonding behavior.

The following examples will serve to illustrate this invention.Percentage figures given are by weight.

Example 1 A mild steel panel was degreased in a conventional manner bytreating with an organic solvent, rinsed with water and then treated atroom temperature for 40 seconds with a solution containing:

35.0% water 7.5% H 0, 57.5% H PO Thereafter the panel was rinsedthoroughly with water and dried. The originally dull steel surface wasbrightened very uniformly and was very well suited for subsequentapplication of a coating.

Example 2 Another mild steel panel was treated as in Example 1 with asolution containing:

40% water 42% H 80 18% B 0,

A very evenlybrightened steel surface, highly suitable for subsequentpaint coating, was obtained.

Example 3 Another mild steel panel was degreased as in Example 1 andthen treated for 60 seconds with a solution containing:

45.5% water 7.3% H 0, 34.4% H PO 12.8% H 80,

Damaged by impact of Panel treated according to this invention" 80inch-pound Panel degreased only 10 inch-pound Panel bonderized 30inch-pound Example 4 Another mild steel panel was treated as in Example2 and coated with a 3 mil thick coating of white alkyd type bakingenamel. Upon impact testing as in Example ,3, it was found that thetreated panel withstood 80 inchpound impact, compared to 10 inch-poundfor a bonderized and 10 inch-pound for a degreased panel.

Example 5 Another steel panel was treated as described in Example 3. Thetreated panel was then electroplated in a Watt's bath and anapproximately 3.5 mil thick nickel coating deposited.

A commercial standard test showed that nickel plate adhesion wasexcellent.

For comparison, a similar untreated panel was prepared for nickelplating by a widely used commercial cleaning procedure comprisingdegreasing, alkaline anodic cleaning, rinsing, acid dipping and rinsing,and then plated in the same way.

This cumbersome multi-step procedure resulted in a nickel plate adheringnot as well to the panel as a nickel plate upon a panel treated inaccordance with this invention.

What is claimed is:

l. The method of improving the bonding properties of mild steel surfaceswhich comprises treating the steel for a period of at least 20 secondswith a solution containing about 20 to weight percent of water, 5 to 30weight percent of H 0 and 25 to weight percent of mineral acid in suchproportions that the sum of percentages of water, H 0, and acid equals100% and then rinsing the steel.

2. The method of claim 1 in which the mineral acid is phosphoric acid. I

3. The method of claim 1 in which the mineral acid is a mixture ofbetween 5 and 20% sulfuric acid and between 95 and phosphoric acid.

4. The method of claim 1 in which the mineral acid is sulfuric acid.

References Cited in the tile of this patent UNITED STATES PATENTS1,911,726 Tanner et a1 May 20, 1933 2,154,451 Hull Apr. 18, 19392,334,699 Faust Nov. 23, 1943 2,511,988 Myers et a1. June 20, 1950

1. THE METHOD OF IMPROVING THE BONDING PROPERTIES OF MILD STEEL SURFACESWHICH COMPRISES TREATING THE STEEL FOR A PERIOD OF AT LEAST 20 SECONDSWITH A SOLUTION CONTAINING ABOUT 20 TO 65 WEIGHT PERCENT OF WATER, 5 TO30 WEIGHT PERCENT OF H202 AND 25 TO 70 WEIGHT PERCENT OF MINERAL ACID INSUCH PROPORTIONS THAT THE SUM OF PERCENTAGES OF WATER, H202 AND ACIDEQUALS 100% AND THEN RINSING THE STEEL.